1. Field
The present application relates to a rotor of a motor and, more particularly, to a rotor constituting a ferrite magnet motor.
2. Background
A vehicle transmission is a mechanism that is manually operated by operation of a clutch by a user or is automatically operated according to a speed. The transmission includes a motor.
As the motor of the transmission, an interior permanent magnet (IPM) motor in which a permanent magnet is buried in a rotor is generally used.
The IPM motor uses a NdFeB permanent magnet that is lightweight and has very strong magnetism, and has high efficiency and output density.
The NdFeB permanent magnet contains neodymium that is a rare-earth element. Due to increases in prices of rare-earth elements, a manufacturing cost of the motor itself is inevitably increased.
For this reason, a recent trend shows that interest is focused on a rare-earth-free motor in which no rare-earth elements are used.
Rare-earth-free motors include a ferrite magnet motor, an induction motor, a reluctance motor, and so on. Among these motors, the ferrite magnet motor is most representative.
The ferrite magnet motor is a motor using a ferrite magnet that is a ceramic magnet. In comparison with the rare-earth motor, the ferrite magnet motor is inexpensive, and is easily designed.
The ferrite magnet motor is generally made up of a ferrite ring magnet having an insertion hole, and a shaft inserted into the insertion hole. The ring magnet and the shaft are fixed by a resin.
Here, the resin is disposed only on a contact region between the shaft and the ring magnet.
For this reason, the ferrite magnet motor provides a low bonding force between the ring magnet and the resin. When the motor is abruptly stopped, the ring magnet is separated from the resin due to inertia of a rotor.
Further, the ferrite magnet is very vulnerable to impact by nature. Since upper and lower surfaces of the ring magnet are exposed to the outside, cracks are frequently generated when the motor is used. Performance of the motor is reduced by leakage from such cracks.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.